Unstable Jan 9th - North Central North Island

Tornado Tim · Unread post by **Tornado Tim** » Wed 08/01/2014 12:26

Looks like a good day for chasing tomorrow, if storms develop on the southerly change, it will be a linear setup, but it will be much more widespread.

Metservice wrote:Valid to: Midnight Thursday 9 Jan 2014

Issued at: 10:46am Wednesday 8 Jan 2014

The central and eastern North Island is expected to be very unstable on Thursday afternoon and evening, with the combination of daytime cloud buildups, a southerly wind change and cold temperatures aloft producing scattered heavy showers and thunderstorms from Waikato and Bay of Plenty through to Gisborne and Hawkes Bay. These thunderstorms will produce localised heavy rain or downpours up to 25mm/hr (or possibly a little higher in some places), and hail of 10-20mm diameter.

A lower risk of thunderstorms covers Northland and northern Auckland in the afternoon, and also a broad area from South Auckland and Coromandel through to northern Taranaki, inland Wanganui and northern Manawatu as indicated on the chart.

In the South Island, daytime cloud buildups should produce scattered showers about Nelson, inland Marlborough and Buller, with a low risk of thunderstorms as indicated on the chart.

No other thunderstorms or significant convection expected over New Zealand on Thursday afternoon and evening.

spwill · Unread post by **spwill** » Wed 08/01/2014 12:40

It is a particularly cold upper level trough for January, should be plenty of hail tomorrow. Hopefully the day is not too messy. I will likely chase.

Tornado Tim · Unread post by **Tornado Tim** » Wed 08/01/2014 13:00

spwill wrote:It is a particularly cold upper level trough for January, should be plenty of hail tomorrow. Hopefully the day is not too messy. I will likely chase.

I will probably Join you.....
PM me your cell and hopefully we can meet up.

jamie · Unread post by **jamie** » Wed 08/01/2014 13:24

There is something i dont particuarly like about this but i cant put my finger on what it is. Perhaps its that i have not seen a setup like this in Jan so i have no experience to call back on.

Perhaps im thinking of this setup as a winter one. In winter we would get a couple of light showers, mostly south of Hamilton. We remain quite dry on a SW. But i suppose being summer there is the extra heat. How about moisture though? In winter the air is more easily saturated. Will there be enough moisture to get a good storm going?

Sorry just thinking outloud there.

jamie · Unread post by **jamie** » Wed 08/01/2014 13:25

I will chase if something shows promise (like a nice linear line)

spwill · Unread post by **spwill** » Wed 08/01/2014 13:46

I think SE of your location Jamie, the southern Hauraki Plains could be a good starting point early tomorrow afternoon. Hoping for plenty of sunshine in between the showers tomorrow.

Tornado Tim · Unread post by **Tornado Tim** » Wed 08/01/2014 14:16

The trop is just shy of 300hpa tomorrow, so any potential Cb's will be of moderate size. Might be worth taking a sweatshirt tomorrow, esp if that southerly is cold.
Hopefully plenty of sunshine tomorrow, any temps over 22 will be very much appreciated

tgsnoopy · Unread post by **tgsnoopy** » Wed 08/01/2014 17:19

Trying to keep the afternoon clear. Will see if I can make it if it looks promising.

treetop · Unread post by **treetop** » Wed 08/01/2014 19:05

coastal BOP may be worth a look as the westerly may run down the coast [under warm conditions hopefully] and provide some good fuel for the incoming S change ,verycold upper level temps should create some additional drama.

Tornado Tim · Unread post by **Tornado Tim** » Wed 08/01/2014 22:26

Updated Outlook:

Metservice wrote: Very unstable conditions are expected to affect the central and eastern North Island on Thursday afternoon and evening, with the combination of daytime cloud buildups, a southerly wind change and cold temperatures aloft producing heavy showers and a high risk of thunderstorms from Waikato and Bay of Plenty through to Gisborne and inland Hawkes Bay as indicated on the map. These thunderstorms will produce localised heavy rain or downpours up to 25mm/hr (or possibly a little higher in some places), and hail of 10-20mm diameter.

A lower risk of thunderstorms covers much of the remainder of the North Island,from Hawkes Bay through the north of Taihape and Taranaki northwards as indicated on the chart.

In the South Island, daytime cloud buildups should produce scattered showers about Nelson, inland Marlborough and Buller, with a low risk of thunderstorms as indicated on the chart.

No other thunderstorms or significant convection expected over New Zealand on Thursday afternoon and evening.

jamie · Unread post by **jamie** » Wed 08/01/2014 22:42

Turns out I'm heading to Taihape tomorrow afternoon so ill try time it that I can drive straight through some action.

jamie · Unread post by **jamie** » Thu 09/01/2014 07:14

Thunder here! Quite a cold nip in the air too.

NZstorm · Unread post by **NZstorm** » Thu 09/01/2014 07:35

I can't recall the last time I saw polar airmass thunderstorms in the Tasman Sea in January!

NZstorm · Unread post by **NZstorm** » Thu 09/01/2014 07:41

Just for the record. 500mb chart for midday.

Manukau heads obs · Thu 09/01/2014 07:45

yes, there was some nice looking CB blown off top anvils just south of me first thing
and one out to the NW of me now
yes a winter looking sky

spwill · Unread post by **spwill** » Thu 09/01/2014 08:00

A 16C start to the day here which is about average but you can see the upper air is very cold with some towering Cu/ Cb in the area. Dewpoint is 13C .

Tornado Tim · Unread post by **Tornado Tim** » Thu 09/01/2014 08:43

jamie wrote:Thunder here! Quite a cold nip in the air too.

Didnt hear that, oh well.....

Seems there is little bit of Lightning in the Storms that have developed in the SW flow.
Certainly shows that the atmosphere is very unstable when there is Lightning early in the morning....

Tornado Tim · Unread post by **Tornado Tim** » Thu 09/01/2014 08:46

Just released Thunderstorm Outlook:

Metservice wrote: A very unstable south to southwesterly flow will cover northern and central New Zealand today, with the combination of cold temperatures aloft, daytime cloud buildups, and a southerly wind change over the central North Island this afternoon and evening producing heavy showers and thunderstorms in many areas.

In Northland, Auckland, and near the west coast from Taranaki northwards, the main risk of thunderstorms is this morning and early afternoon, with the thunderstorm activity easing by evening. Brief heavy rain and hail will accompany these thunderstorms.

Over the central North Island from Waikato and Bay of Plenty southwards to the central high country and Hawkes Bay, there is a high risk of thunderstorms this afternoon and evening, mostly on a southerly wind change. These thunderstorms will be accompanied by localised heavy rain, squally winds and hail. Over eastern Bay of Plenty, Rotorua, Taupo, and inland Hawkes Bay and Gisborne, a few of these thunderstorms are likely to be severe with localised downpours of 25-40mm/hr and larger hail.

A low risk of thunderstorms covers all other North Island areas from northern Manawatu northwards through the day.

In the South Island, there is a low to moderate risk of thunderstorms about Nelson, Buller and western Marlborough, with the main risk of thunderstorms about the Nelson area this afternoon. Localised heavy rain and hail will accompany these storms.

No other thunderstorms or significant convection expected over New Zealand today.

Manukau heads obs · Thu 09/01/2014 08:51

I am up for a chase...maybe I could get join up at bombay...let me know...time to meet

jamie · Unread post by **jamie** » Thu 09/01/2014 08:58

what time will this southerly move up? Ill try time my trip south so im in tirau area ready for it. Does 3pm at tirau sound safe?

NZstorm · Unread post by **NZstorm** » Thu 09/01/2014 09:05

Unfortunately its a big drive from Auckland down to the thunderstorm zone which looks south and east of Tirau.

Surface southerly creeps up during the afternoon. A sea breeze in the BOP would spice up convection there.

Tornado Tim · Unread post by **Tornado Tim** » Thu 09/01/2014 09:08

I am up for a South Waikato Chase.... Hopefully it goes off this time, other times I have chased a high risk and it came to nothing, LOL

Manukau heads obs · Thu 09/01/2014 09:08

yeah...I did wonder about having to drive that far south...

jamie · Unread post by **jamie** » Thu 09/01/2014 09:13

NZstorm wrote:Surface southerly creeps up during the afternoon. A sea breeze in the BOP would spice up convection there.

Just done some looking and the southerly is on Palmerston Norths door step right now. Doesnt look to be moving all that fast.

But the 12z GFS shows it at taupo by 1pm. Well into BOP at 4pm.

Oh yes a sea breeze there will really get things going!

NZstorm · Unread post by **NZstorm** » Thu 09/01/2014 09:15

GFS surface wind chart for 4pm today.

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